Electronic devices, especially portable terminal devices, such as portable telephones, have included an operation section illuminated by, e.g. light-emitting diodes or EL elements to identify push buttons and display sheets even in dark environments Light guide sheets and movable contact assemblies used in such devices have been required to permit various illuminations inexpensively.
FIGS. 6 and 7 are a sectional view and a plan view of a conventional switch 501 described in JP2009-99298A. Base 1 has a film shape and has a light-transmissive property. Plural protruding illuminating sections 2 are provided on a lower surface of base 1, thus forming light guide sheet 3.
A predetermined portion of an outer periphery of base sheet 4 is attached to a lower surface of light guide sheet 3 with an adhesive. Movable contact 5 has substantially a dome shape and is made of an electrically conductive thin metal sheet. Plural movable contacts 5 are attached to a lower surface of base sheet 4 beneath illumination sections 2, thus forming movable contact assembly 6.
Circuit board 7 has plural wiring patterns formed on upper and lower surfaces thereof. Plural fixed contacts 8 are provided on the upper surface of circuit board 7. Fixed contacts 8 include central fixed contact 8A having substantially a circular shape and outer fixed contacts 8B substantially a horseshoe or ring shape surrounding central fixed contact 8A.
A predetermined portion of an outer periphery of movable contact assembly 6 is attached to the upper surface of circuit board 7 with adhesive layer 9. An outer periphery of movable contact 5 is placed on outer fixed contacts 8B. The center of the lower surface of movable contact 5 faces central fixed contact 8A with a predetermined gap.
Light emitter 10 is implemented by a light source, such as a light emitting diode. Plural light emitters 10 are mounted on the upper surface of circuit board 7 at the side of light guide sheet 3. Light emitter 10 has a light-emitting surface facing an edge surface of cutout 11A at an edge of base 1. Reflection sheet 11 is attached so as to cover the upper surface of cutout 11A and light emitter 10. Reflection sheet 11 is made of film having light-reflective material, such as aluminum, vapor-deposited thereon.
Display sheet 12 is light-transmissive and has a film shape. Light blocking section 112A is formed on the lower surface of display sheet 12 by, for example, printing. Predetermined portions of light blocking section 112A are punched out in shapes of, for example, characters or symbols, thus forming plural display sections 112B. Display sections 112B are disposed on the upper part of illumination sections 2 of light guide sheet 3, thus providing switch 501.
Switch 501 is mounted on an operation surface of an electronic device, such as a portable telephone. Plural central fixed contacts 8A, outer fixed contacts 8B, and plural light emitters 10 are connected to an electric circuit of the electronic device via wiring patterns.
An operation of conventional switch 501 will be described below. When a predetermined display section 112B of display sheet 12 is pressed down, light guide sheet 3 and base sheet 4 that are located below the pressed section bend downward, thereby pressing down the dome-shaped central part of movable contact 5. When a predetermined pressing power is applied, movable contact 5 is elastically reversed downward with a click feeling, causing the center of the lower surface of movable contact 5 to contact central fixed contact 8A. Thus, central fixed contact 8A and outer fixed contacts 8B are connected electrically via movable contact 5.
Furthermore, when the downward pressure to display sheet 12 is released, movable contact 5 is elastically reversed upward by an elastic returning force, causing the center of the lower surface of movable contact 5 to depart from central fixed contact 8A. Thereby, central fixed contact 8A and outer fixed contacts 8B are electrically disconnected from each other.
According to such electrical connection and disconnection of fixed contacts 8, functions of the electronic device are switched. When electric power is supplied to light emitters 10 from the electronic circuit of the electronic device according to such electrical connection and disconnection of fixed contacts 8, plural light emitters 10 emit light. The light enters into light guide sheet 3 from the edge surface thereof and transmits inside base 1 while it is reflected.
The light is further reflected from plural illumination sections 2 to illuminate display sections 112B from below. Since plural display sections 112B are illuminated, a user can identify the displayed characters and symbols on display section 112B even in dark environments, and thus can executing out operations easily.
In conventional movable contact assembly 6 and switch 501, in order to prevent light from leaking to the upper part of light emitter 10, plural reflection sheets 11 as separate components are attached on the upper surfaces of cutouts 11A and light emitters 10 at an edge of base 1. Therefore, the number of components is increased, and the time required for assembly is increased. As a result, switch 501 becomes more expensive.